Typically, filter elements are comprised of a filter media which separates particles from a stream of fluid and support structure for the filter media. More specifically, air filters which utilize pleated annular filter media have an internal supporting tube with perforations or holes therethrough which fits in the hollow core of the filter media and provides an internal support. In addition, end caps are provided which fit over radially extending axial ends of the filter media and are held in place by end cap adhesive, which adhesive also seals the space between panels forming the pleats of the filter media. When air flows from outside the filter media to the hollow core of the filter media, the perforated tube, which may be expanded metal, supports the filter media and keeps the filter media from collapsing. The end caps and end cap adhesive close the pleats so that air does not bypass the filter media by flowing between the pleats.
Some filter elements have an external protective structure or support such as an expanded metal sleeve which fits around the outside of the filter media and protects the filter media from external impacts. There are a number of difficulties with external expanded metal sleeves, one of which is the expense of stocking various widths and heights of expanded metal external sleeves which, with some difficulty, must be sheared to very close tolerances in order to meet specification and which must be rolled to mimic a round outside diameter and then welded to that specific diameter. Another difficulty is that expanded metal has many sharp edges that cut employees and customers. An additional drawback is that the sharp edges scrape the filters and can result in filter tears which cause dusting problems in engines or other equipment which require clean air. While the filter is protected from external impacts of large objects, the occasional tear, due to the sharp edges of standard metal sleeves, is a disadvantage which results from utilizing the sleeves.
As industries become increasingly aware of efficiency, users of heavy duty dust collectors need outer wraps which are more open so as to minimize interference with air flow into the filter media. This is especially the case for filter installations in which filters are cleaned by a blast of high volume back pulse air from the clean side or inner side of the filter. The back pulse extends the life of the filters by removing, in many cases, substantially all particles and contaminants from the pleats of the filter media. In the filters with an exterior expanded metal sleeve, there is not enough open space to disperse the dust away from the pleats because the expanded metal tends to confine the dust.